But the front-runner came under criticism over a Texas immigration plan to grant tuition aid to children of illegal immigrants, a position that could hurt him among conservatives.

Polls show Perry and Romney are way ahead of the other seven candidates in the debate in the race to be the Republican nominee to face Democratic President Barack Obama in 2012.

Republicans increasingly see a good chance to remove Obama from the White House, with the US economy struggling to rebound from 9.1 per cent unemployment and chronic debt and deficits.

On a day the stock market plunged on fears of renewed recession, the US economy was the top topic and all the candidates promised conservative prescriptions to fix it, and declared Obama's economic leadership a failure.

Romney's book

Perry said Romney first wrote in a book that a healthcare plan he introduced in Massachusetts was exactly what the American people needed, but took the line out in the book's later, paperback edition when criticism of the reform grew.

And Perry accused Romney of backing Obama's Race to the Top education plan which violates conservative principles of getting the federal government out of US public education.

Romney and Michele Bachmann, the Minnesota congresswoman, accused Perry of coddling illegal immigrants with a Texas policy to allow their children to gain education tuition assistance.

"I would not allow taxpayer-funded benefits to illegal aliens or for their children," Bachmann said. "That's a magnet. End the magnets for illegal aliens to come into the United States of America."

Perry said that as the governor of a state with a long border with Mexico, no one worked harder than he did on border security. He fiercely defended the programme as correct for his state, saying to do nothing would leave the immigrant children as a burden.

To those who oppose it, he said, "I don't think you have a heart. We need to be educating these children because they will be a drag on our society."

Immigration is a sensitive topic in Republican politics.

Senator John McCain's support for a reform plan in 2007 nearly ended his 2008 presidential bid.